When people earn BTC from sig campaigns, they spend some of them mostly in gambling sites, some even save then spend them in cloud mining contracts (don't know why, most of those don't get you a ROI), others go to the market place and trade them for cash and the rest do altcoin trades. That's overall good as BTC changes hands a lot.
You do realize that the useless content that is produced by them is the reason for which people with actual knowledge regarding Bitcoin stay away from this forum? I couldn't care less about the few bucks that these spammers make and what they do with it. There are campaigns that do not care about this problem (e.g. BitMixer); thus the need to punish services that endorse spam.
That's why a good move from Bitcointalk would be to ban all sig campaigns in all sections in the forum except the Bitcoin and Altcoin market places imo. And even then the mods should pressure the campaign managers to have stricter rules and to recruit only people who make good posts. I think I remember you in the Betcoin sig campaign before, not sure. But the guy who used to run it, Ros, was a really good manager and recruiter. The campaign actually made me improve my posts. He's a good example of an excellent campaign manager. If a sig campaign cannot produce good posts for a set amount of time, warn the manager or else ban that particular campaign altogether. They should clean up their act.
But what good will that bring? It will kill the small economy we have going on here.
Yes, it will bring a lot of good and no, it won't kill the economy. The people that do trades of value are usually not signature spammers.
It won't kill the economy, no. But you know what I mean. It's a metaphor for it will really affect the forum's economy's growth. Again from what I have observed, Bitcointalk is evolving into a commerce board where BTC are changing hands day by day. And that's cool that a simple machines forum has the potential to achieve so much more. Don't hinder it. Earning BTC from sig campaigns is not a bad thing.